There exists a continuing need to improve semiconductor device performance and to further scale semiconductor devices. A characteristic that limits scalability and device performance is electron and hole mobility, also referred to as channel mobility, throughout the channel region of transistors. As devices continue to shrink in size, the transistor channel regions also shrink in size. This can limit channel mobility.
One technique that may improve downward scaling limits and device performance is to introduce strain into the channel region, which can improve electron and hole mobility. Different types of strain, including expansive strain, uniaxial tensile strain, and compressive strain, have been introduced into channel regions in order to determine their effect on electron and/or hole mobility.
The introduction of the stress can be accomplished by first placing a stress inducing layer, such as a nitride or oxide layer, over completed gate structures. The device is then subjected to an anneal process at temperatures that exceed 1000° C. This not only incorporates stress into the channel region of the transistors, but it is also sufficient to activate the dopants located within source/drains.
It has been realized, however, that this temperature stress inducing process also creates dislocations within the channel region of the semiconductor substrate. Dislocations occur when crystallographic planes within the substrate shift slightly and create a path along which mid-level states and dopant segregation can occur. These mid-level states and this dopant segregation can create a conductive path between the source and drain, which causes a short that renders the transistor inoperative.
Some stress inducing processes have been developed by the semiconductor industry to combat this problem, but these processes typically involve multiple and complex processing steps that are both costly and time-consuming.
Accordingly, what is needed is a semiconductor device and method of manufacturing that device that provides the required amount of stress but reduces the formation of dislocations between the source/drain.